Tubular heater terminal seal



Oct. 31, 1950 J. POUCHNIK ETAL TUBULAR HEATER TERMINAL SEAL Filed March21, 1949 )9 Y k b. w ll/47% I w w M w w W ,4

Patented Oct. 31, 1950 TUBULAR HEATER TERMINAL SEAL Lawrence J.Pouchnik, Milwaukee, andJerome B. Welch, Wauwatosa, Wis., assignorstoCutler-Hammer, Inc., Milwaukee, Wis., a corporation of DelawareApplication March 21, 1949, Serial N0. 82,586

7 Claims.

' This invention relates to electric heaters and more particularly to animproved method and means for sealing the terminal ends of heatershaving tubular enclosing sheaths.

- It is a primary object of the present invention toprovide for sealingthe terminal ends of such heaters in a simple and expeditious manner.

Another object is to provide for sealing in such a manner that gasesthat may be generated within the heater during the process of sealingcannot render the resulting seals imperfect.

Another object is to provide terminal end seals which are impervious toliquids, moisture, vapors and gases.

Another object is to provide a terminal end seal which is characterizedby unusual electrical resistivity, mechanical toughness and strength.

Other objects and advantages of the invention will hereinafter appear.

The accompanying drawings illustratean embodiment of the invention whichwill now be described; it being understood that the embodiment issusceptible of various modifications without departing from the scope ofthe appended claims.

In the drawings:

Figure 1 is a view in longitudinal section of a portion of a tubulartype heater prior to application of a terminal seal; the terminal leadand the resistor being. shown in elevation.

Figure 2 is similar to Fig. 1, but shows thehe'ater at one stage duringthe application of a terminal seal. 7

Figs. 8 and 4 show the heater at successively later stages during theapplication of a terminal seal, and show processing apparatus which maybe employed, and

Fig. 5 is a fragmentary sectional view showing the terminal seal in acompleted state; the terminal lead being shown in elevation.

Referring to Fig. 1, it shows a tubular type electric heater comprisinga helical resistor 6" which is embedded in a compacted mass ofrefractory insulating material 1, such as magnesium oxide, and incasedby a tubular sheath 8 of any preferredcross-sectional form. The resistor6 is connected in any preferred manner to a terminal lead 9 whichextends outwardly of sheath 8'. The sheath adjacent its end is unfilledand provides a recess Ill to receive the terminal seal.

The heater as shown in Fig. 1 is ready for apgreater percentage of themoisture entrained in theinsulating material 1. Further iti's assumedthat in preparation for improved terminal seal the inner surface of thesheath 8 surrounding recess ID has been suitably cleaned.

. Referring to Fig. 2, a quantity of suitable vitre' ous material I l inpowdered form is placed in=the recess l 0 in such amount that saidrecess is completely filled. It has been found that vitreous materialssuitable for use with the sealing process to be hereinafter describedare preferably of the pro-fused type wherein the component constituentssubstantially all go into solution to provide a homogeneous mixturewhich is amorphous'in:

character.

As the character of the resulting terminal seal depends to a greatextent upon the character of the component constituents of the materialll, care should be exercised in the selection of such constituents. Whensuch material is subsequently re-fused and solidified into a solid mass,thematerial should have a coefficient of linear thermal expansionclosely approximating that of the materials of which the sheath 8 andthe terminal lead 9 are formed and should retain its solidity at thetemperatures attained by the terminal end portions of the heater whenthe latter is energized. Further, when so re-fused and solidified, suchmaterial should have relatively high electrical resistivity and beresistant to mechanical 1 breakage. There are several commerciallyavailable vitreous materials which will meet the above recitedrequirements and which will provide satthe application of the isfactoryterminal seals when treated in accordance with themethod now to bedescribed in detail. However, applicants havefound that a cer-' tainvitreous composition described in the appli-- cation of Fred H.Kaufmann, Serial No. 73,673,-

flled January 29, 1949, and issued as Patent No. 2,527,884 on even dateherewith, is preferred as a sealing medium. The constituents of thepreferred vitreous composition and percentages of each by weight basedon the total weight of such composition as given in Table III of theaforementioned application are as follows:

The material ll may be placed in recess 10' in any convenient manner; anexpeditious way of doing this being to force the end of the heater intoa powderedmass of such material as by hand so as to cause the materialto be forced into and completely fill recess I0 in a semi-compactedstate.

3 Then the portion of sheath 8 coextensive with recess I is subjected tolocalized heating to effect fusion and/or liquefaction of the material iI. Such heating may be done in any preferred way, for example, bysubjecting such portion of sheath 8 to the heat of a plurality of gasfiames.

When the material II has become re-fused and has attained a homogeneousliquid or plastic conan intermediate member I4, a shaft I 5, andcoolsistency, heating of the sheath 8 is terminated and a pressureplunger or punch I2, shown in Figs. 3 and 4, is fitted over the terminallead 9 and moved downwardly and inwardly of the recess I0 so as to exertpressure on the fused but unsolidified matreial which in Fig. 4 isdesignated I l instead of II in view of its altered state. The pressureapplied by the punch I2 on the material II should be on the order of2100 pounds per square inch and the duration of such pressure need notexceed two or three seconds. Punch I2 during such operation should bemaintained at ordinary room temperature, and preferably lower, to insurethat the material II will not stick or adhere to the punch.

Application of the aforementioned amount of pressure on the fused butunsolidified material I I in the manner aforedescribed elfects areduction in the volume of such material to substantially one-half itsoriginal volume, thus densifying the same to a large degree. Suchdensification of the material I l eliminates any voids or pockets whichmay form as an incident to re-fusion the material. Further, therelatively cool pressure applying punch tends to effect rapidsolidification of the material II into a solid body designated II Whilesome gases may be generated in the insulating material I as a result ofthe heating of the sheath 8 as aforedescribed and would have a tendencyto form bubbles or pin holes in the material II during solidification,the counteracting pressure and rapid solidifying action imparted by thepunch I2 prevents this from occurring.

After completion of the aforementioned pressure applyin operation on thematerial II and after the latter has solidified, the solid fusedVitreous body II results in the recess II] of the heater, the punch I2preferably being shaped to afford the body II the form shown in Fig. 5.The body II thus formed strongly adheres in a bonded relation to theinner surface of sheath 8 and to the terminal lead 9 and provides asealed barrier against the ingress or egress of moisture, vapors orgases into or from the insulating material I. Assuming that thecomposition of the material I I initially used in the sealing operationmeets the requirements aforementioned, the resulting seals will retaintheir bond and solidity at the temperatures attained by the terminal endportions of the heaters when the latter are energized. The preferredvitreous composition aforementioned, if used as the sealing medium inconnection with the sealing process hereinbefore described, results interminal seals which meet all of the aforementioned requirements and inaddition have unusually high electrical resistivity, on

the order of 61 megohms at 760 F., and unusual mechanical toughness,being able to withstand mechanical shocks on the order of 2000 footfoundto be highly satisfactory in applyingthe,

ant conducting conduits I6 and IT. The punch I2 is preferably made ofhardened steel. Block I3 is made of a high heat conducting metal such ascopper. With the punch I2, block I3, member I4, and conduits I6 and Ilformed and assembled as shown, a chamber I8 is provided in which acooling medium such as water may be circulated by virtue of the conduitsI6 and IT. Continuously subjecting the punch l2 to influence ofcirculating water at ordinarysupply temperatures will insure that inrepeated pressure applying operations the material II will not stick oradhere to the punch and rapid solidification of such material will befacilitated.

We claim:

1. The method of sealing the terminal end of an electric heater whereina resistor enclosed in an open end tubular sheath is embedded ininsulation terminating at a distance from the end of the sheath to leavethe sheath with an open end recess, and wherein the resistor has aterminal portion projecting through said recess to a point beyond thesheath, which comprises filling the end recess with a vitreous materialin powdered form, heating locally the end of the sheath to fuse saidmaterial, and subjecting said material in fused but unsolidified stateto pressure on the a point beyond the sheath, which comprises fillingthe end recess with a vitreous material in powdered form, heatinglocally the end of the sheath to fuse said material, and subjecting saidmaterial in fused but unsolidified state to pressure on the order of2,100 pounds per square inch at least briefly while permitting saidmaterial to cool, maintaining in a relatively cool state the pressureapplying means.

3. The method of sealing the terminal end of an electric heater whereina resistor enclosed in an open end tubular sheath is embedded ininsulation terminating at a distance from the end of the sheath to leavethe sheath with an open end recess, and wherein the resistor has aterminal portion projecting through said recess to a point beyond thesheath, which comprises forcing the end portion of the heater into apowdered mass of vitreous material to effect filling of the end recesswith said material in a semi-compacted state, heating locally the end ofthe sheath to fuse said material, and subjecting said material infusedbut unsolidified state to pressure on the order of 2,100 pounds persquare inch at least briefly while permitting said fused material tocool, maintaining in a relatively cool state the pressure applyingmeans.

4. The method of sealing the terminal end of an electric heater whereina resistor enclosed in an open end tubular sheath is embedded ininsulation terminating at a distance from the end of the sheath to leavethe sheath with an open end recess, and wherein the resistor has aterminal portion projecting through said recess to a point beyond thesheath, which comprises filling the end recess with a vitreouscomposition in powdered form, said composition having as itsconstituents by weight based on the total weight.

of such composition, 27.68% silica, 7.33% boric oxide, 18.76% fluorspar,37.69% barium oxide, 5.63% zinc oxide, 1.92% alumina and 0.99% cobaltoxide, heating locall the end of the sheath to fuse said powderedcomposition, and subjecting said composition in fused but unsolidifiedstate to pressure on the order of 2,100 pounds per square inch at leastbriefly while permitting said composition to cool, maintaining in arelatively 0001 state the pressure applying means.

5. The combination with a tubular heater comprising a resistor having aterminal portion, an open end tubular sheath surrounding said resistorand also its terminal portion in part, and insulation in said sheathretaining said resistor in spaced relation to said sheath, saidinsulation terminating at a distance from the end of said sheath leavingsaid sheath with an open end recess through which said terminal portionprojects, of a seal for the terminal end of said heater comprising asolidified body of vitreous material occupying at least a portion of therecess in said sheath and adhering in bonded relation with said sheathand said terminal portion, said vitreous material consisting of a fusedmixture of 27.68% silica, 7.33% boric oxide, 18.76% fluorspar, 37.69%barium oxide, 5.63% zinc oxide, 1.92% alumina and 0.99% cobalt oxide.

6. The method of sealing the terminal end of an electric heater whereina resistor enclosed in an open end tubular sheath is embedded ininsulation terminating at a distance from the end of the sheath to leavethe sheath with an open end recess, and wherein the resistor has aterminal projecting through said recess to a point beyond the sheath,which comprises filling the end of the sheath with a vitreous materialin powdered form, heating said vitreous material in situ to fuse thesame, and subjecting said material in fu ed but unsolidified state tomechanical pressure on the order of 2,100 pounds per square inch atleast briefly while permitting the material to cool. 1

7. The combination with a, tubular heater comprising a resistor having aterminal portion, an open end tubular sheath surrounding said resistorand also its terminal portion in part, and insulation in said sheathretaining said resistor in spaced relation to said sheath, saidinsulation terminating at a distance from the end of said sheath leavingsaid sheath with an open end recess through which said terminal portionprojects, of a seal for the terminal end of said heater occupying atleast a, portion of the recess and adhering in bonded relation to saidsheath and said terminal portion, said seal consisting of a homogeneousmass of solidified vitreous material formed in situ of a vitreouscomposition Of the pre-fused type by re-fusion and application of arelatively high degree of mechanical pressure thereto at least brieflyduring solidification.

LAWRENCE J. POUCHNIK. JEROME B. WELCH.

REFERENCES CITED The following ref rences are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,043,196 Finlayson June 2, 1936FOREIGN PATENTS Number Country Date 577,748 Great Britain May 30, 1946

